Bi-modal (also known as "prime-boost") immunization takes advantage of the diverse responses generated by immunogens presented in different contexts. These include innate responses to different adjuvants and vectors, as well as antigen-specific responses resulting from different antigen presentation pathways. In recent years, effort has been focused on generating cell-mediated immunity (CMI) by the use of non-replicating viral vectors, such as MVA or replication-defective adenovirus, and DMAvaccines. However, the importance of humoral responses, including broadly reactive neutralizing antibodies and antibody- dependent cellular cytotoxicity (ADCC) activities, has been increasingly recognized. Therefore, it is necessary to explore prime-boost strategies likely to induce both CMI and humoral responses. An attractive strategy is exemplified by priming with replication-competent viral vectors (e.g., adenovirus) expressing multiple HIV antigens, followed by boosting with subunit protein immunogens, as proposed in this Program Project. The overall goal of this Core is to provide investigators in Projects 2 and 3 with recombinant subunit proteins, including HIV-1 clade C gp160, SIV Gag-Pol particles, as well as recombinant SIVmac239 Nef protein. The specific aims of this Core are: (1) To express, characterize and purify clade C HIV-1 envelope glycoprotein gp160 from recombinant vaccinia viruses; (2) To express, characterize and purify SIVmac239 Gag-Pol particles from recombinant vaccinia viruses; (3) To express, characterize and purify SIVmac239 Nef from recombinant E. coli.